package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {
        MappedStatement mappedStatement = getMappedStatement(statementid);
        List<Object> list = getSimpleExecutor().query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public int insert(String statementid, Object param) throws Exception {
        return update(statementid, param);
    }

    @Override
    public int update(String statementid, Object param) throws Exception {
        MappedStatement mappedStatement = getMappedStatement(statementid);
        return getSimpleExecutor().update(configuration, mappedStatement, param);
    }

    @Override
    public int delete(String statementid, Object param) throws Exception {
        return update(statementid, param);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回

        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

                /*
                底层都还是去执行JDBC代码，根据不同情况来调用selctList/selectOne/insert/update/delete
                 */
                // 被代理对象的方法名
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();

                // 准备参数1：statmentid：sql语句的唯一标识，"namespace.id" 即 "接口全限定名.方法名"
                String statementId = className + "." + methodName;

                // 准备参数2：params:args
                // 获取被调用方法的返回值类型
                Type genericReturnType = method.getGenericReturnType();

                // 判断是否进行了 泛型类型参数化
                if (genericReturnType instanceof ParameterizedType) {
                    List<Object> objects = selectList(statementId, args);
                    return objects;
                }

                // 这里简单使用了switch做方法识别
                switch (methodName) {
                    case "insert":
                        return insert(statementId, args[0]);
                    case "update":
                        return update(statementId, args[0]);
                    case "delete":
                        return delete(statementId, args[0]);
                    default:
                        return selectOne(statementId, args);
                }

            }
        });

        return (T) proxyInstance;
    }

    /**
     * 根据 statementId 获取 MappedStatement
     *
     * @param statementId
     * @return
     */
    private MappedStatement getMappedStatement(String statementId) {
        return configuration.getMappedStatementMap().get(statementId);
    }

    /**
     * 获取 SimpleExecutor
     *
     * @return
     */
    private SimpleExecutor getSimpleExecutor() {
        return new SimpleExecutor();
    }


}
